1. Field of the Invention
The invention relates in general to the method and the apparatus of controlling an optical disc drive, and more particularly to the method and the apparatus of controlling the tilt-angle of lens in the optical pick-up head.
2. Description of the Related Art
Optical storage media such as CD-ROM, CD-RW, and DVD-ROM, with the features of low cost and large storage space, have been widely used in various kinds of audio/video data storage, data backup, and etc.
FIG. 1 is a diagram of a carriage in an optical disc drive. The carriage 100 includes an optical pick-up head 110, a guide rod 102, 104, a spindle motor 106, and a sled motor 108. When accessing data from the optical disc, the spindle motor 106 rotates the optical disc, and the optical pick-up head 110 is driven by the sled motor 108 to shift along the guide rods 102 and 104, i.e., to shift along the radial direction of the optical disc to locate a corresponding track.
FIG. 2A is a sectional view of an optical pick-up head. The optical pick-up head 110 includes a sled 112, a lens 114, a support wire 116, and at least an actuator (not shown in the diagram). The sled 112 shifts along the guide rods 102 and 104. The lens 114 is hung in the sled via the support wire 116. By controlling the current supplied to the actuator, the lens 114 is controlled to shift along the radial direction to achieve a precise tracking. When performing a tracking on process, the lens 114 is shifted first without the sled 112 moved, and only when the lens 114 has reached the border of the sled 112, will the sled 112 move to access the following tracks.
However, when the lens 114 shifts from the center of the sled 112, a tilt-angle will be formed as shown in FIG. 2B and will affect the focusing of the laser beam. Moreover, in a DVD recorder that is becoming more and more popular today, the numerical aperture (NA) of the lens is about 65-67, which is higher than that of the lens in a DVD-ROM drive. Therefore, the tilted lens has even more negative influence on the quality of accessed data in a DVD recorder.